The present invention relates to a method and apparatus for determining the mass flow through an engine, the present invention relates in particular to a method and apparatus for determining the mass flow through a gas turbine engine.
There is a requirement for determining the total mass flow through the core engine of a gas turbine engine. The fuel flow to a gas turbine engine is already measured, but the airflow through the gas turbine engine is difficult to measure.
Accordingly the present invention seeks to provide a novel method and apparatus, which reduces, preferably overcomes, the above-mentioned problems.
Accordingly the present invention provides a method for determining the total mass flow through an engine comprising measuring the fuel flow to the engine, measuring the concentration of carbon dioxide, measuring the ratio of water to oxygen, measuring the ratio of carbon dioxide to oxygen or measuring the ratio of water to carbon dioxide in the gases exhausted in the engine from the fuel flow and the concentration of carbon dioxide, the ratio of water to oxygen, the ratio of carbon dioxide to oxygen or the ratio of water to carbon dioxide, determining the air mass flow through the engine from the air to fuel ratio and calculating the total air and fuel mass flow through the engine by adding the air mass flow through the engine to the fuel mass flow to the engine.
Measuring the concentration of carbon dioxide may comprise detecting infrared radiation emitted by carbon dioxide in the gases exhausted from the engine and determining the concentration of carbon dioxide.
Preferably measuring the concentration of carbon dioxide comprises detecting infrared radiation absorbed by carbon dioxide in the gases exhausted from the engine and determining the concentration of carbon dioxide.
Preferably measuring the ratio of water to oxygen comprises detecting infra-red radiation absorbed by water in the gases exhausted from the engine, detecting near infra-red radiation absorbed by oxygen in the gases exhausted from the engine, determining the concentration of water, determining the concentration of oxygen and calculating the ratio of water to oxygen.
Preferably measuring the ratio of carbon dioxide to oxygen comprises detecting infra-red radiation absorbed by carbon dioxide in the gases exhausted from the engine, detecting near infra-red radiation absorbed by oxygen in the gases exhausted from the engine, determining the concentration of carbon dioxide, determining the concentration of oxygen and calculating the ratio of carbon dioxide to oxygen.
Preferably measuring the ratio of water to carbon dioxide comprises detecting infrared radiation absorbed by water in the gases exhausted from the engine, detecting infrared radiation absorbed by carbon dioxide in the gases exhausted from the engine, determining the concentration of water, determining the concentration of carbon dioxide and calculating the ratio of water to carbon dioxide.
Preferably the method comprises irradiating the gases exhausted from the engine with a light.
Preferably the method comprises irradiating the gases exhausted from the engine with a laser light.
Preferably the method comprises detecting infrared radiation absorbed or emitted by the gases exhausted from the engine at a plurality of lines across the exhaust of the engine.
The method may comprise moving a detector. The method may comprise moving a light source.
Alternatively the method comprises moving at least one mirror.
Preferably the engine is a gas turbine engine. More preferably the engine is a turbofan gas turbine engine.
Accordingly the present invention also provides an apparatus for determining the total mass flow through an engine comprising means for measuring the fuel flow to the engine, means for measuring the concentration of carbon dioxide, means for measuring the ratio of water to oxygen, means for measuring the ratio of carbon dioxide to oxygen or means for measuring the ratio of water to carbon dioxide in the gases exhausted from the engine, means for determining the air to fuel ratio in the engine from the fuel flow and the concentration of carbon dioxide, the ratio of water to oxygen, the ratio of carbon dioxide to oxygen or the ratio of water to carbon dioxide, means for determining the air mass flow through the engine from the air to fuel ratio and means for calculating the total air and fuel mass flow through the engine by adding the air mass flow through the engine to the fuel mass flow to the engine.
Preferably the engine is a gas turbine engine. More preferably the gas turbine engine is a turbofan gas turbine engine.
Preferably the means for measuring the concentration of carbon dioxide comprises at least one detector. Preferably the detector comprises a spectrometer and a photo-detector, the spectrometer is optically coupled to the photo-detector. Preferably the spectrometer is a Fourier transform spectrometer.
Preferably the means for measuring the concentration of carbon dioxide comprises a light source. Preferably the light source is a laser. The laser may be a tunable laser. Preferably the laser is a diode laser. There may be a plurality of lasers. The lasers may be tuned to different wavelengths, there are means to switch the lasers on sequentially.
Preferably there are means to scan the gases exhausted from the engine. The means to scan may comprise one or more mirrors.